OK. You have the date wrong, sorry. The 12 over a C in a diamond or rhombus was used from 1898-1924. It was nitro proofed.
You can find the proof marks and some trade marks here:
http://damascus-barrels.com/bp.html

I can find nothing on the JH in a circle. I will keep looking.

With the slings and check piece, I am guessing it was made for the German market.

Pete